Fetal Blood Sampling or Intrauterine Transfusion

Fetal blood sampling (FBS) is a procedure in which a thin needle, similar to the needle used for amniocentesis, is inserted into one of the fetal vessels under ultrasound guidance. Through this needle, the fetal medicine specialist obtains a small blood sample from the fetus. When the fetus has too little red blood cells or platelets, the same needle can be used to inject red blood cells or platelets into the fetus. This is called a transfusion.

FBS and IUT’s are done using local anaesthesia (freezing injected into the skin). The mother can also receive intravenous (IV) medication help her to remain relaxed, but not to go to sleep during the procedure.. When transfusions are done under planned circumstances, we ask mothers to fast (i.e. NOTHING to eat or drink) for at least 8 hours prior to the procedure.

Often the fetus will also receive some medication during the procedure to prevent it from moving during transfusion.

Before fetal viability (~ 24 weeks), fetal blood sampling and intrauterine transfusions are done on an outpatient basis; after viability, the mother is admitted to hospital for a few hours, however can usually go home a few hours after the procedure.

In such cases, after viability, we usually suggest giving the mother 2 shots of intramuscular steroids 24 hours apart to help mature the fetal lungs.

For what conditions are fetal blood sampling or intrauterine transfusion done?

Fetal blood sampling is done when the fetus is at risk for anemia or thrombocytopenia (too little red blood cells or platelets). Sometimes a fetal blood sample can also be obtained to determine the fetal karyotype.

What are the risks of FBS or IUT for the fetus?

In experienced hands, FBS is technically successful in 97% of cases. The risk of breaking the water after the procedure or preterm labor is less than 2% for fetal blood samples done in the third trimester of pregnancy, but may be higher for FBS done prior to 22 weeks of gestation. Depending on the reason why FBS is done, additional risks may be present. These are discussed under the specific conditions. Mount Sinai hospital has the largest program for fetal blood sampling and transfusion in Canada and one of the largest and most experienced in the world.

What are the risks of FBS or IUT for the mother?

The risk of infection after FBS or IUT is very small. Usually antibiotics are administered preventatively prior to an IUT, but not prior to FBS. We do know that FBS and IUT’s do not damage the uterus. A previous FBS is not a reason to deliver a baby by caesarean section. FBS does not affect a mother’s long-term health or her future fertility.